The present invention relates to the field of electromagnetic relays, and in particular to an electromagnetic relay in which a movable block assembly which actuates a contact mechanism is movable along a direction perpendicular to the axial line of the iron core of the relay.
Conventionally, there is a per se known form of electromagnetic relay in which a movable block which actuates a contact mechanism is movable along a direction perpendicular to the axial line of the iron core of the relay. Such a movable block, in the prior art, has been supported by being engaged to a movable contact member. This is done in order to minimize mechanical contact resistance. A problem with this has been that, as the movable block moves, it tends to wobble and to be woggled, i.e. undergoes slight rotary motion, as it moves along its proper direction of motion perpendicular to the axial line of the iron core of the relay. However, nowadays with the increasing demands for reduction in size and weight of electromagnetic relays, even a slight such wobbling motion of the movable block may cause the contact pressure of the contact mechanism to be altered, and may cause fluctuations in the amount of magnetic coupling between the movable block and an electromagnetic block of the relay including said iron core thereof, and this can produce the problem that accurate operating and restoring voltages are not maintained.
Another problem that has arisen with electromagnetic relays is the following. Typically, the movable block has driven a movable contact member so as to cause it to cooperate with a pair of fixed contact members which are provided as opposing to one another, for engagement and/or disengagement of contacts. However, again with the increasing demands for reduction in size and weight of electromagnetic relays which are being made nowadays, because of the tendency for the distance between the iron core of the relay and the contacts of the contact mechanism to change due to deformation in the base structure of the relay, such as for instance can be caused due to thermal stress, thereby the stroke of the motion of the movable block of the relay may be altered, and also the contact pressure of the contact mechanism has a tendency to change. According to this, again, the problem that accurate operating and restoring voltages are not maintained is exacerbated.
Further, if the distance between the iron core of the relay and the contacts of the contact mechanism is reduced in view of the desirability of making the relay more compact, then the distance available for providing electrical insulation between said iron core of the relay and said contacts of the contact mechanism is reduced.
Another problem with such an electromagnetic relay relates to its method of manufacture. When a fixed terminal piece supporting the aforementioned movable contact member and the aforementioned pair of fixed contact members which are to be provided as mounted to the base structure of the relay as opposing to one another, and when these members are formed from one sheet of metal with a so called lead frame and are then to be insert molded in said base structure of the relay, it is necessary to avoid opposing relationship other than between said contact members, and, as proposed for instance in Japanese Patent Laying Open Publication Ser. No. 56-143631 (1981), one of the fixed contact members can be provided sideways away from the longitudinal direction of the movable contact member, in relation to the other fixed contact member. If this fixed contact member is offset sideways in this manner, in a multiple pole type electromagnetic relay of the above described type in which the movable contact member is driven by a movable block, the problem arises that the fixed contact member tends to obstruct the movement of the movable block, and, in order to ensure sufficient space for the movement of the movable block, the fixed contact member must be mounted rather far towards the outside of the electromagnetic relay, thus creating the need to increase the space assigned thereto, and preventing the electromagnetic relay of this type from being acceptably compact.
Further, when the set distance between the electromagnetic block of the relay including the iron core thereof and the contact mechanism is reduced, for the purpose of reducing the overall size of the electromagnetic relay and increasing its compactness, an arc barrier wall must be provided as projecting outwards from the base assembly of the relay for insulating these members from one another, and it becomes difficult to form the arc barrier wall integrally with the base assembly at the same time as insert molding the movable contact member and the two fixed contact members together therewith, thus undesirably increasing the cost for manufacture of the electromagnetic relay.